See; www.spiderorchid.com/mesoamerica/mesoamerica.htm
where evidence is provided to suggest that:
The Long count is a lunar calendar.
The Accounting year of 364 days might be considered a Venus calendar.
104 years is the natural and optimum intercalation time to correct the
solar and Venus calendars - and is the basis of the Mesoamerican
Calendar Round.
Robert Peden